This invention relates generally to a perforated plate of a steam reforming valve for reducing the pressure of steam at high temperature and high pressure, at the same time mixing the steam with water thereby to reduce the steam temperature, and thus reforming the steam into low temperature and low pressure steam. More specifically, the invention relates to a perforated plate installed in a steam reforming valve of the above defined class and operating when the steam mixed with water passes therethrough to agitate the mixture.
In a steam reforming valve for reforming steam at high temperature and high pressure into steam at low temperature and low pressure, in general, steam mixed with water is further agitated and rendered into uniform low temperature and low pressure steam. For this purpose, a perforated plate having numerous through-holes is provided in the valve.
When steam at high temperature and water which have not yet been mixed throughly pass through a perforated plate, high temperature steam and water at low temperature impinge on the surface of the perforated valve and cause great temperature differences to occur at various parts of this perforated plate surface. As a consequence, these parts of the perforated plate fixed to the main structure of the steam reforming valve undergo expansion and contraction, whereby thermal stresses develop. As a result, the perforated plate is subjected to fatigue and, if these thermal stresses become excessive, will be damaged.
Particularly in the prior art, perforated plates of this character have been of a construction wherein numerous holes are merely formed in a disc part, which is fixed to the casing structure of a steam reforming valve. For this reason, deformations due to temperature differences are not relieved or absorbed, whereby thermal stresses will occur and there has been the problem of damage and breakage due to thermal stresses.